This invention relates to a two-cylinder thick-matter pump according to the preamble of claim 1.
Two-cylinder thick-matter pumps consist of two single pumps which are linked by circuit technology and synchronized in their motion sequence in such a way that while one cylinder (Z1) pumps the other cylinder (Z2) executes a suction stroke. Usually, the reciprocating speeds of the pistons are equal in both cylinders so that the ending times of the cylinder strokes (suction stroke and pumping stroke) coin-cide. The direction of motion of the cylinder pistons is reversed at the end of each stroke so as to effect constant alternation between pumping and suction strokes.
The suction stroke serves to convey thick matter such as concrete from a priming tank to the particular sucking cylinder. In the subsequent pumping stream the previously sucked-in material is urged out of the now pumping cylinder into the delivery pipe. To ensure that this process always takes place properly one usually provides one or more controllers or reversing valvesxe2x80x94for example diverter valves or flat slide valvesxe2x80x94which move back and forth between two end positions in order to establish the right connection between the cylinder openings, the delivery pipe connection and the priming tank.
Diverters, the currently most common controllers, are generally so disposed as to swivel back and forth between two end positions in which they establish the necessary connection between the cylinder openings, the delivery pipe connection and the priming tank. The diverter is constantly connected at one end with the delivery pipe while the other end covers the cylinder opening of the particular pumping cylinder. The cylinder opening of the sucking cylinder is thus open to the priming tank.
Since the reversing process of the diverter from one cylinder opening to the other cannot be effected at any desired speed, the flow of material in the delivery pipe is interrupted upon a change of stroke. This necessarily results in a discontinuous flow of material with problematic consequences such as acceleration shocks, surges, high mechanical loads on the components, oscillations in a possibly connected distributing boom, increased wear, etc.
Further adverse effects can prolong the flow interruptions further. For example one often observes the effect that the sucked-in thick matter is compressible because of its air or gas content. At the onset of the pumping stroke the thick matter must thus first be precompressed to the operating pressure prevailing in the delivery pipe before the flow of material commences. Depending on the kind of concrete and in accordance with the other operating conditions, however, the necessity of precompression can also be negligibly small.
Another kind of flow interruption is especially problematic, however. It results from the fact that diverters of the above-described kind and arrangement do not completely cover the delivery cylinder openings at the same time in the center position during their shifting motion (this effect being known as xe2x80x9cnegative coverxe2x80x9d). The thick matter pressurized and prestressed in the delivery pipe can thereby flow back into the cylinder filled with as yet uncompressed thick matter, or past its opening into the priming tank (this effect being known as a xe2x80x9cshort circuitxe2x80x9d).
Altogether, the above-described effects lead to a considerable temporal interruption of the flow of material in the delivery pipe and possibly also to a considerable reduction of output due to return flow out of the delivery pipe. One can lessen the adverse effects by accelerating the shifting motion, but not completely eliminate them.
There is thus a desire to avoid interruptions in the flow of material and to deliver concrete continuously. The prior art already shows several attempted solutions for this but they are either insufficiently operable or involve unreasonable constructional effort making the pumps too expensive and uneconomical.
According to one idea, the piston speeds in the delivery cylinders are dimensioned differently, e.g. the suction speed is selected so much greater than the pumping speed that the suction stroke is ended early enough for the diverter to swivel as far as the center position between the two cylinders in the remaining time until the end of the pumping stroke. A plurality of phases are thereby passed through, in the first of which the cylinder opening of the previously sucking cylinder is closed by means of a shut-off element so that the pressurized concrete cannot flow back into the priming tank in any phase. Closing the cylinder opening additionally permits thick matter located in the cylinder to be precompressed to the operating pressure prevailing in the delivery pipe. In a further swivel phase the opening of the previously sucking cylinder is likewise connected with the delivery pipe, while the pumping stroke of the other cylinder is still ongoing. The cylinder filled with pre-compressed thick matter remains in this position (pump standby position) up to the end of the pumping stroke and then starts its own pumping stroke without a time delay and without a pressure drop in the delivery pipe, while in a third phase the opening of the previously pumping cylinder is initially closed by means of a further shut-off element (to avoid a short circuit). in a fourth and last phase the opening of said cylinder to the priming tank is released and the cylinder, or the piston of this cylinder, begins its suction stroke, again at a higher speed than that of the ongoing pumping stroke. The end of the suction stroke is followed by a new reversing process of the diverter, again while the pumping stroke in the reverse direction is still ongoing.
According to a furtherknown solution from the applicant, described in DE 29 09 964 to Schwing, each delivery cylinder is assigned its own diverter for controlling the suction and pumping stream while avoiding back flow and permitting precompression. A shut-off plate integrally formed as a shut-off element laterally on the inlet opening of the diverter prevents back flow and permits the precompression stroke. The outlet ends of the diverters open into a forked pipe whose outlet communicates with the delivery pipe. This pump is particularly worthy of improvement with respect to its overall width, constructional expense (two diverters, i.e. double material expense) and energy consumption (double expenditure of energy for the two swivel drives of the diverters).
The generic U.S. Pat. No. 3,663,129 proposes realizing the control of the thick-matter stream of a continuous-flow two-cylinder thick-matter pump with only one diverter. In contrast to DE 29 09 964, the pump of U.S. Pat. No. 3,663,129 has only one diverter passed by the pressurized stream, but its outsized inlet opening is problematic. It extends in an oblong shape over the arc of the swivel radius and must have a length corresponding to at least three times the diameter of the delivery cylinder openings since both cylinders must be connected with the delivery pipe in an intermediate phase (pump standby position of the previously sucking cylinder).
The high forces occurring at the usual high operating pressures cannot be absorbed by this diverter and the priming tank receiving the diverter, except with extremely great wall thickness. This is exacerbated by the fact that very high inertia forces and moments also result from the necessary short swivel times over the long shifting paths. From a static point of view as well, the excess weight of the usually mobile pumps resulting from the great wall thickness is unacceptable, as are the high costs.
The invention therefore aims to provide a continuous-flow two-cylinder thick-matter pump with low constructional expense.
The invention achieves this goal by the subject of claim 1.
Continuous-flow thick-matter pumps known from the prior art have in common that their development has long kept to disposing the diverter in the bottom area of the priming tank in the usual way and giving the diverter the function of guiding the pumping (pressurized) stream from the cylinders to the delivery pipe. The invention surprisingly takes a different path because it disposes the diverter between the suction side of the delivery cylinders and the suction pipe and separates the priming tank functionally from the diverter housing. The invention thus realizes a simple and compact diverter for controlling continuous thick-matter flow in a simple way. The inventive diverter thus requires only one circular opening with the diameter of the suction pipe at its end sweeping over the cylinder openings.
The invention further provides an especially compact arrangement wherein the diverter is disposed in a very small separate housing having a xe2x80x9cminimalxe2x80x9d geometry, so to speak, whereby the side lengths of the housing are only slightly longer than the diameter of the pipe and cylinder openings. The housing is constantly under delivery pressure, whereby the cavity between the outside contour of the diverter and the inside contour of the housing acts in a simple way as a pressure line and connects the particular pumping cylinder with the delivery pipe.
In contrast to the generic prior art (U.S. Pat. No. 3,663,129), the diverter is not disposed on the pumping side but on the suction side. This avoids the problems of an outsize design of the diverter outlet as a result of the high pressures in the delivery pipe as compared with the generic prior art.
It is known from DE-AS 16 53 614 to dispose a diverter controlling thick matter in a separate housing, the diverter guiding the thick-matter flow (suction stream) from the priming tank to the cylinders. However, the pump shown in this print is unsuitable for delivering thick matter continuously. To make this clearer, mention is first made of Swiss patent application CH 8986/61 or U.S. Pat. No. 3,146,721 which show the prior art DE-AS 16 53 614 wants to improve. CH 8986/61 describes a hydraulic piston pump for delivering viscous, pulpy or plastic materials. The piston pump comprises a cylindrical valve slide with two actuate channels which rotate to connect the material inlet and the material outlet alternately with one of the delivery cylinders. The material flow necessarily comes to a temporary standstill when the valve slide is located in an intermediate position.
DE-AS 16 53 614 wants to improve this prior art by providing a rotary slide valve for a sludge pump with no temporary interruption occurring in the material stream. The solution of DE-AS 16 53 614 achieves this by a cuplike valve box with three openings in the side wall and by a cuplike valve gate whose bottom part is located in the vicinity of the bottom part of the valve box and has two wings. The cup-like valve gate connects a priming tank with one of the cylinders at a time. The cup-like valve gate is thus in the widest sense a xe2x80x9cdiverterxe2x80x9d disposed on the suction side. But this diverter only prevents material from standing still temporarily under the pressure effect upon disturbances in the synchronism between valve slide and delivery cylinder (apparently a control problem of that time) because the material outlet constantly remains open. Continuous pumping is not possible, nor is it mentioned anywhere in the print. For example, with knowledge of the present invention it is clear that the suction side of the valve of DE 16 53 614 is lacking a shut-off element for preventing back flow.
The present invention, in contrast provides the generic thick-matter pump with a reversing valve whose diverter is connected on the suction side but which nevertheless permits continuous pumping. This is due to, among other things, the additional shut-off element for closing the suction pipe and/or the first and/or second openings of the diverter housing, which reliably prevents thick matter from flowing back into the suction pipe or even into the priming tank. This measure is not known from DE 16 53 614.
A further problem of DE 16 53 614 is that the shown valve is heavy and extremely costly in terms of material. This is another reason why the idea of DE 16 53 614, i.e. the idea of a suction-side diverter, was never taken up to realize a continuous-flow pump.
The combined features of claim 1, however, make it possible to realize a very compact reversing valve whose geometric dimensions can be astonishingly minimized. One reason for this is that no great pressure differences occur on the shut-off elements of the reversing valve to load said components excessively. During reversal there are ideally no pressure differences at all on the shut-off elements.
To control the pump or its valve one preferably uses the abovementioned method, making the piston speeds in the delivery cylinders different and selecting the suction speed so much greater than the pumping speed that the suction stroke is ended early enough for the diverter to already start swiveling in the remaining time up to the end of the pumping stroke. A plurality of phases are again passed through. For details reference is made to the description of the figures.
Advantageous variants of the invention are stated in the subclaims.